For an image formation by way of a photographic technique, there has been employed a photosensitive composition containing a photosensitive component such as diazonium salts, azides or quinonediazides, or a photohardening composition containing a photocrosslinkable component. Most of these compositions are sensitive to ultraviolet light, but not sensitive to visible light.
Scanning exposure techniques employing laser beams, however, have recently progressed so that it is desired to develop a photopolymerizable composition which is sensitive to visible light such as an argon laser. A composition containing a thioxanthene dyestuff which is sensitive to light of up to 600 nm is proposed and intensely studied.
In the field of laser beams, a semiconductor laser has become more popular instead of a gas laser(e.g. argon laser or helium-neon laser), because the semiconductor laser is cheap and does not need a complicated apparatus in comparison with the gas laser. Also, it is intensely studied that the wave length of a laser beam from the semiconductor laser is shifted to a visible light region from a near infrared region and in the near future the use of 600 to 700 nm will be possible. As a material sensitive to visible light of 600 to 700 nm, silver salt photography and electrophotography are exemplified. They, however, have defects in coating workability and resolving power. It is desirable to develop a material without having the above defects, that is, a photopolymerizable composition which is sensitive to visible light having a long wave length.